Gas turbine engines, also known as combustion turbine engines, are rotary engines that extract energy from a flow of combusted gases passing through the engine onto a multitude of turbine blades. Gas turbine engines have been used for land and nautical locomotion and power generation, but are most commonly used for aeronautical applications such as for airplanes and helicopters, where they primarily are used for propulsion.
Gas turbine engines usually also power a number of different accessories such as generators, starter/generators, permanent magnet alternators (PMA) and/or permanent magnet generators (PMG), fuel pumps, and hydraulic pumps. All these accessories provide for functions needed on the aircraft other than propelling the aircraft. For example, when a gas turbine engine is running, the starter generator (S/G) produces electrical power, some of which may be stored; when the gas turbine engine needs to be started, the S/G functions as a starting motor when provided energy from another energy source, such as the previously stored electrical power.
Typically, an accessory gearbox is included with a gas turbine engine, and has a main gearbox housing for receiving a plurality of gears to drive the different accessories. Accessory gearboxes are expensive, heavy, take up a lot of space, have many unique parts, generate heat, leak oil, require scavenges, churn oil, require many special processes, and require endurance and fire testing for certification. An accessory gearbox is typically one of the heaviest components on an engine, ranging from 30 to 300 pounds. Further, the accessory gearbox is also one of the most expensive components with very large tooling costs. Further, the accessory gearbox can include hundreds of unique parts. The number of parts can drive manufacturer supply chain issues.